System and Method for Facilitating Observation of Monitored Physiologic Data

ABSTRACT

Present embodiments are directed to a system and method capable of detecting and graphically indicating physiologic patterns in patient data. For example, present embodiments may include a monitoring system that includes a monitor capable of receiving input relating to patient physiological parameters and storing historical data related to the parameters. Additionally, the monitoring system may include a screen capable of displaying the historical data corresponding to the patient physiological parameters. Further, the monitoring system may include a pattern detection feature capable of analyzing the historical data to detect a physiologic pattern in a segment of the historical data and capable of initiating a graphical indication of the segment on the screen when the physiologic pattern is present in the segment.

CROSS REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 14/103,265, filed Dec. 11, 2013, which is a continuation ofU.S. patent application Ser. No. 12/609,314, filed Oct. 30, 2009, nowU.S. Pat. No. 8,622,916, which claims priority to U.S. ProvisionalPatent Application No. 61/110,259, filed Oct. 31, 2008, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates generally to user-interface applicationsfor patient monitoring devices. In particular, present embodimentsrelate to display features that facilitate observation of monitoredphysiological data with patient monitoring instruments.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Patient monitors include medical devices that facilitate measurement andobservation of patient physiological data. For example, pulse oximetersare a type of patient monitor. A typical patient monitor cooperates witha sensor to detect and display a patient's vital signs (e.g.,temperature, pulse rate, or respiratory rate) and/or other physiologicalmeasurements (e.g., water content of tissue, or blood oxygen level) forobservation by a user (e.g., clinician). For example, pulse oximetersare generally utilized with related sensors to detect and monitor apatient's functional oxygen saturation of arterial hemoglobin (i.e.,SpO₂) and pulse rate. Other types of patient monitors may be utilized todetect and monitor other physiological parameters. The use of patientmonitors may improve patient care by facilitating supervision of apatient without continuous attendance by a human observer (e.g., a nurseor physician).

A patient monitor may include a screen that displays informationrelating to operation and use of the patient monitor. A typical patientmonitor screen may display patient data for further interpretation by auser. For example, a pulse oximetry monitor may display data in the formof a plethysmographic waveform or in the form of a numeric index, suchas an oxygen saturation value. However, while a monitor may conveyinformation to a user about the patient's condition, such informationmay be difficult to interpret quickly.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of present embodiments may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 is a perspective view of an exemplary patient monitor;

FIG. 2 is a perspective view of the exemplary patient monitor in asystem with separate devices;

FIG. 3 is a representation of an exemplary display including a trend ofphysiological data that exhibits a detected pattern;

FIG. 4 is an exemplary block diagram of an electronic device;

FIG. 5 is an exemplary graph of SpO₂ trend data with an upper band andlower band based on mean and standard deviation values;

FIG. 6 is an exemplary graph including an SpO₂ trend that contains aventilatory instability SpO₂ pattern and a trend of the resultingsaturation pattern detection index;

FIG. 7 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 8 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 9 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 10 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 11 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 12 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 13 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 14 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 15 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 16 is an exemplary display including a graphical indicator relatedto ventilatory instability;

FIG. 17 is an exemplary display of a menu related to alarm managementand settings for alarms related to ventilatory instability;

FIG. 18 is an exemplary display of a menu related to alarm managementand settings for alarms related to ventilatory instability;

FIG. 19 is an exemplary display of a menu related to alarm managementand settings for alarms related to ventilatory instability; and

FIG. 20 is an exemplary flow chart of a process for alarm management foralarms related to ventilatory instability.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

Present embodiments may facilitate observation of certain events (e.g.,SpO₂ patterns) displayed on a monitor's user-interface by providinggraphic indicators that relate to the status of certain features.Further, present embodiments may include one or more graphic featuresthat are actively representative of a status of pattern detection or alevel (e.g., a percentage of an alarm level) of a detected occurrence.Such graphic features may provide an active representation of a gradualbuild up of indicators that correspond to identification of a particularpattern or that are indicative of a severity level of an identifiedcondition. Indeed, present embodiments may utilize an accumulation ofdata indicators to identify a physiologic pattern or a severity level ofa particular event, and the graphic feature may gradually change asobserved indications accumulate. For example, in accordance withembodiments, ventilatory instability may be detected when a number ofcertain data features have been detected within a time period. Thus, apercentage value associated with ventilatory instability detection maybe identified by dividing the number of detected data features by thenumber utilized for identification of a ventilatory instability pattern,and the percentage may be represented in a dynamic graphic (e.g., astatus bar). As a specific example, a graphic displayed as a triangleoutline may gradually fill in the triangle outline from the bottom ascertain indicators of a particular pattern accumulate. Thus, thetriangle graphic may be completely filled in when the pattern isactually confirmed. Likewise, the triangle may empty when certainaspects are reduced. Similarly, a graphic may gradually fill or empty ascertain severity thresholds or indexes of a particular event arereached.

FIG. 1 is a perspective view of a patient monitor 10 in accordance withan exemplary embodiment of the present disclosure. Specifically, thepatient monitor 10 illustrated by FIG. 1 is a pulse oximeter that isconfigured to detect and monitor blood oxygen saturation levels, pulserate, and so forth. It should be noted that while the illustratedembodiment includes a pulse oximeter, other embodiments may includedifferent types of patient monitors 10. For example, the patient monitor10 may be representative of a vital signs monitor, a critical caremonitor, an obstetrical care monitor, or the like.

The illustrated patient monitor 10 includes a front panel 12 coupled toa body 14 of the monitor 10. The front panel 12 includes a displayscreen 16 and various indicators 18 (e.g., indicator lights and displayscreen graphics) that facilitate operation of the monitor 10 andobservation of a patient's physiological metrics (e.g., pulse rate).Some of the indicators 18 are specifically provided to facilitatemonitoring of a patient's physiological parameters. For example, theindicators 18 may include representations of the most recently measuredvalues for SpO₂, pulse rate, index values, and pulse amplitude. Inembodiments, the indicators 18 may include an indicator related toventilatory instability. In an embodiment, the indicator 18 may be atriangular indicator that is related to an index of ventilatoryinstability determined by the monitor 10. When the index increases, thetriangle fills from bottom to top. In an embodiment, the indicator 18may be a Sat Seconds indicator that provides an indication related tolow oxygen saturation. Other indicators 18 may be specifically providedto facilitate operation of the monitor 10. For example, the indicators18 may include an A/C power indicator, a low battery indicator, an alarmsilence indicator, a mode indicator, and so forth. The front panel 12may also include a speaker 20 for emitting audible indications (e.g.,alarms), a sensor port 22 for coupling with a sensor 24 (e.g., atemperature sensor, a pulse oximeter sensor) and other monitor features.

Additionally, the front panel 12 may include various activationmechanisms 26 (e.g., buttons and switches) to facilitate management andoperation of the monitor 10. For example, the front panel 12 may includefunction keys (e.g., keys with varying functions), a power switch,adjustment buttons, an alarm silence button, and so forth. It should benoted that in other embodiments, the indicators 18 and activationmechanisms 26 may be arranged on different parts of the monitor 10. Inother words, the indicators 18 and activation mechanisms 26 need not belocated on the front panel 12. Indeed, in some embodiments, activationmechanisms 26 are virtual representations in a display or actualcomponents disposed on separate devices.

In some embodiments, as illustrated in FIG. 2, the monitor 10 maycooperate with separate devices, such as a separate screen 28, awireless remote 30, and/or a keyboard 32. These separate devices mayinclude some of the indicators 18 and activation mechanisms 26 describedabove. For example, buttons 34 on the remote 30 and/or keyboard 32 mayoperate as activation mechanisms 26. Specifically, for example, thebuttons 34 may cause the monitor 10 to perform specific operations(e.g., power up, adjust a setting, silence an alarm) when actuated onthe separate device. Similarly, the indicators 18 and/or activationmechanisms 26 may not be directly disposed on the monitor 10. Forexample, the indicators 18 may include icons, indicator lights, orgraphics on the separate screen 28 (e.g., a computer screen). Further,the activation mechanisms 26 may include programs or graphic featuresthat can be selected and operated via a display. It should be noted thatthe separate screen 28 and/or the keyboard 32 may communicate directlyor wirelessly with the monitor 10.

FIG. 3 is a representation of a display 180 that includes a trend 182 ofoxygen saturation over time. As illustrated in FIG. 3, the monitor 10may detect a cluster or pattern 184 of desaturation data, which themonitor 10 may determine is likely indicative of sleep apnea or someother issue. The monitor 10 may then label the pattern 184 with atextual graphic 186 and a timestamp 188 indicating a beginning and endof the detected pattern 184. Further, the monitor 10 may highlight orflash the pattern, as indicated by block 190, or utilize some othergraphical indicator. In addition, the monitor may display an indicatorthat may provide information to a clinician that provides informationthat may be related to a patient condition. For example, the clinicianmay use present embodiments to simply snap or jump to a displayincluding the pattern 184 (e.g., indication of sleep apnea orventilation instability) by activating the display control feature(e.g., pressing a button), and the graphic indicators may draw the usersattention to facilitate diagnosis.

In order to graphically or textually indicate the patterns in SpO₂ trenddata (e.g., saturation patterns indicative of ventilatory instability),as discussed above, the patterns must first be detected. Accordingly,present embodiments may include code stored on a tangible,computer-readable medium (e.g., a memory) and/or hardware capable ofdetecting the presence of a saturation pattern in a series ofphysiologic data. For example, FIG. 4 is a block diagram of anelectronic device or pattern detection feature in accordance withpresent embodiments. The electronic device is generally indicated by thereference number 200. The electronic device 200 (e.g., an SpO₂ monitorand/or memory device) may comprise various subsystems represented asfunctional blocks in FIG. 4. Those of ordinary skill in the art willappreciate that the various functional blocks shown in FIG. 4 maycomprise hardware elements (e.g., circuitry), software elements (e.g.,computer code stored on a hard drive) or a combination of both hardwareand software elements. For example, each functional block may representsoftware code and/or hardware components that are configured to performportions of an algorithm. Specifically, in the illustrated embodiment,the electronic device 200 includes a reciprocation detection (RD)feature 202, a reciprocation qualification (RQ) feature 204, a clusterdetermination (CD) feature 206, a saturation pattern detection index(SPDi) calculation feature 208, and a user notification (UN) feature210. Each of these components and the coordination of their functionswill be discussed in further detail below.

It should be noted that, in order to detect certain data patterns,embodiments of the present disclosure may utilize systems and methodssuch as those disclosed in U.S. Pat. No. 6,760,608, U.S. Pat. No.6,223,064, U.S. Pat. No. 5,398,682, U.S. Pat. No. 5,605,151, U.S. Pat.No. 6,748,252, U.S. application Ser. No. 11/455,408 filed Jun. 19, 2006,U.S. application Ser. No. 11/369,379 filed Mar. 7, 2006, and U.S.application Ser. No. 11/351,787 filed Feb. 10, 2006. Accordingly, U.S.Pat. No. 6,760,608, U.S. Pat. No. 6,223,064, U.S. Pat. No. 5,398,682,U.S. Pat. No. 5,605,151, U.S. Pat. No. 6,748,252, U.S. application Ser.No. 11/455,408 filed Jun. 19, 2006, U.S. application Ser. No. 11/369,379filed Mar. 7, 2006, and U.S. application Ser. No. 11/351,787 filed Feb.10, 2006 are each incorporated herein by reference in their entirety forall purposes.

The RD feature 202 may be capable of performing an algorithm fordetecting reciprocations in a data trend. Specifically, the algorithm ofthe RD feature 202 may perform a statistical method to find potentialreciprocation peaks and nadirs in a trend of SpO₂ data. A nadir may bedefined as a minimum SpO₂ value in a reciprocation. The peaks mayinclude a rise peak (e.g., a maximum SpO₂ value in a reciprocation thatoccurs after the nadir) and/or a fall peak (e.g., a maximum SpO₂ valuein a reciprocation that occurs before the nadir). Once per second, theRD feature 202 may calculate a 12 second rolling mean and standarddeviation of the SpO₂ trend. Further, based on these mean and standarddeviation values, an upper band 220 and lower band 222 with respect toan SpO₂ trend 224, as illustrated by the graph 226 in FIG. 5, may becalculated as follows:

Upper Band=mean+standard deviation;

Lower Band=mean−standard deviation.

Once the upper band 220 and lower band 222 have been determined,potential reciprocation peaks and nadirs may be extracted from the SpO₂trend 224 using the upper band 220 and the lower band 224. Indeed, apotential peak may be identified as the highest SpO₂ point in a trendsegment which is entirely above the upper band 220. Similarly, apotential nadir may be identified as the lowest SpO₂ point in a trendsegment that is entirely below the lower band 222. In other words, peaksidentified by the RD feature 202 may be at least one standard deviationabove the rolling mean, and nadirs identified by the RD feature 202 maybe at least one standard deviation below the mean. If there is more thanone minimum value below the lower band 222, the last (or most recent)trend point may be identified as a nadir. If more than one maximum valueis above the upper band 220, the point identified as a peak may dependon where it is in relation to the nadir. For example, regardingpotential peaks that occur prior to a nadir (e.g., fall peaks) the mostrecent maximum trend point may be used. In contrast, for peaks thatoccur subsequent to a nadir (e.g., rise peaks), the first maximum pointmay be used. In the example trend data represented in FIG. 5, a peak andnadir is detected approximately every 30-60 seconds.

In one embodiment, a window size for calculating the mean and standarddeviation may be set based on historical values (e.g., average durationof a set number of previous reciprocations). For example, in oneembodiment, a window size for calculating the mean and standarddeviation may be set to the average duration of all qualifiedreciprocations in the last 6 minutes divided by 2. In anotherembodiment, an adaptive window method may be utilized wherein the windowsize may be initially set to 12 seconds and then increased as the lengthof qualified reciprocations increases. This may be done in anticipationof larger reciprocations because reciprocations that occur next to eachother tend to be of similar shape and size. If the window remained at 12seconds, it could potentially be too short for larger reciprocations andmay prematurely detect peaks and nadirs. The following equation orcalculation is representative of a window size determination, whereinthe output of the filter is inclusively limited to 12-36 seconds, andthe equation is executed each time a new reciprocation is qualified:

If no qualified reciprocations in the last 6 minutes:

Window Size=12(initial value)

else:

RecipDur=½*current qualified recip duration+½*previous RecipDur

Window Size=bound(RecipDur,12,36).

With regard to SpO₂ signals that are essentially flat, the dynamicwindow method may fail to find the three points (i.e., a fall peak, arise peak, and a nadir) utilized to identify a potential reciprocation.Therefore, the RD feature 202 may limit the amount of time that thedynamic window method can search for a potential reciprocation. Forexample, if no reciprocations are found in 240 seconds plus the currentadaptive window size, the algorithm of the RD feature 202 may timeoutand begin to look for potential reciprocations at the current SpO₂ trendpoint and later. The net effect of this may be that the RD feature 202detects potential reciprocations less than 240 seconds long.

Once potential peaks and nadirs are found using the RD feature 202, theRQ feature 204 may pass the potential reciprocations through one or morequalification stages to determine if a related event is caused byventilatory instability. A first qualification stage may includechecking reciprocation metrics against a set of limits (e.g.,predetermined hard limits). A second qualification stage may include alinear qualification function. In accordance with present embodiments, areciprocation may be required to pass through both stages in order to bequalified.

As an example, in a first qualification stage, which may include alimit-based qualification, four metrics may be calculated for eachpotential reciprocation and compared to a set of limits. Anyreciprocation with a metric that falls outside of these limits may bedisqualified. The limits may be based on empirical data. For example, insome embodiments, the limits may be selected by calculating the metricsfor potential reciprocations from sleep lab data where ventilatoryinstability is known to be present, and then comparing the results tometrics from motion and breathe-down studies. The limits may then berefined to filter out true positives.

The metrics referred to above may include fall slope, magnitude, sloperatio, and path length ratio. With regard to fall slope, it may bedesirable to limit the maximum fall slope to filter out high frequencyartifact in the SpO₂ trend, and limit the minimum fall slope to ensurethat slow SpO₂ changes are not qualified as reciprocations. Regardingmagnitude, limits may be placed on the minimum magnitude because ofdifficulties associated with deciphering the difference betweenventilatory instability reciprocations and artifact reciprocations asthe reciprocation size decreases, and on the maximum magnitude to avoidfalse positives associated with sever artifact (e.g., brief changes ofmore than 35% SpO₂ that are unrelated to actual ventilatoryinstability). The slope ratio may be limited to indirectly limit therise slope for the same reasons as the fall slope is limited and becauseventilatory instability patterns essentially always have a desaturationrate that is slower than the resaturation (or recovery) rate. The pathlength ratio may be defined as Path Length/((Fall Peak−Nadir)+(RisePeak−Nadir)), where Path Length=Σ|Current SpO₂ Value−Previous SpO₂value| for all SpO₂ values in a reciprocation, and the maximum pathlength ratio may be limited to limit the maximum standard deviation ofthe reciprocation, which limits high frequency artifact. The followingtable (Table I) lists the above-identified metrics along with theirassociated equations and the limits used in accordance with oneembodiment:

TABLE I Metric Equation Minimum Maximum Fall Slope (Nadir − FallPeak)/Time −1.6 (Fast Response −0.08 (Fast Response between Fall Peakand Nadir Mode) Mode) −1 (Normal Response −0.05 (Normal Mode) ResponseMode) Magnitude Max(Rise Peak, Fall Peak) − 3 35 Nadir Slope |FallSlope/Rise Slope| 0.05 1.75 Ratio Path Path Length = Σ|Current N/A 2Length SpO2 Value − Previous SpO2 Ratio Value)| for all SpO2 values in aReciprocation. Path Length Ratio = Path Length/((Fall Peak − Nadir) +(Rise Peak − Nadir))

As indicated in Table I above, an oximetry algorithm in accordance withpresent embodiments may operate in two response modes: Normal ResponseMode or Fast Response Mode. The selected setting may change the SpO₂filtering performed by the oximetry algorithm, which in turn can causechanges in SpO₂ patterns. Therefore a saturation pattern detectionfeature may also accept a response mode so that it can account for thedifferent SpO₂ filtering. Table I indicates values associated with bothtypes of response mode with regard to the Fall Slope values.

A second qualification stage of the RQ feature 204 may utilize a objectreciprocation qualification feature. Specifically, the secondqualification stage may utilize a linear qualification function based onease of implementation, efficiency, and ease of optimization. Theequation may be determined by performing a least squares analysis. Forexample, such an analysis may be performed with MATLAB®. The inputs tothe equation may include the set of metrics described below. The outputmay be optimized to a maximum value for patterns where ventilatoryinstability is known to be present. The equation may be optimized tooutput smaller values (e.g., 0) for other data sets where potentialfalse positive reciprocations are abundant.

To simplify optimization, the equation may be factored into manageablesub-equations. For example, the equation may be factored intosub-equation 1, sub-equation D, and sub-equation 2, as will be discussedbelow. The output of each sub-equation may then be substituted into thequalification function to generate an output. The outputs from each ofthe sub-equations may not be utilized to determine whether areciprocation is qualified in accordance with present embodiments.Rather, an output from a full qualification function may be utilized toqualify a reciprocation. It should be noted that the equations set forthin the following paragraphs describe one set of constants. However,separate sets of constants may be used based on the selected responsemode. For example, a first set of constants may be used for the NormalResponse Mode and a second set of constants may be used for the FastResponse Mode.

Preprocessing may be utilized in accordance with present embodiments toprevent overflow for each part of the qualification function. The tables(Tables II-VII) discussed below, which relate to specific components ofthe qualification function may demonstrate this overflow prevention.Each row in a table contains the maximum value of term which is equal tothe maximum value of the input variable multiplied by the constant,wherein the term “maximum” may refer to the largest possible absolutevalue of a given input. Each row in a table contains the maximumintermediate sum of the current term and all previous terms. Forexample, a second row may contain the maximum output for the second termcalculated, as well as the maximum sum of terms 1 and 2. It should benoted that the order of the row may match the order that the terms arecalculated by the RQ feature 204. Further, it should be noted that inthe tables for each sub-equation below, equations may be calculatedusing temporary signed 32-bit integers, and, thus, for each row in atable where the current term or intermediate term sum exceeds 2147483647or is less than −2147483647 then an overflow/underflow condition mayoccur.

A first sub-equation, sub-equation 1, may use metrics from a singlereciprocation. For example, sub-equation 1 may be represented asfollows:

Eq1Score=SlopeRatio*SrCf+PeakDiff*PdCf+FallSlope*FsCf+PathRatio*PrCf+Eq1Offset,

where SrCf, PdCf, FsCf, PrCf, and Eq1Offset may be selected using leastsquares analysis (e.g., using MATLAB®). PeakDiff may be defined as equalto |Recip Fall Peak−Recip Rise Peak|. It should be noted that PeakDiffis typically not considered in isolation but in combination with othermetrics to facilitate separation. For example, a true positivereciprocation which meets other criteria but has a high peak differencecould be an incomplete recovery. That is, a patient's SpO₂ may drop froma baseline to a certain nadir value, but then fail to subsequentlyrecover to the baseline. However, when used in combination with othermetrics in the equation, PeakDiff may facilitate separation of twoclassifications, as large peak differences are more abundant in falsepositive data sets.

With regard to sub-equation 1, the tables (Tables II and III) set forthbelow demonstrate that the inputs may be preprocessed to preventoverflow. Further, the tables set forth below include exemplary limitsthat may be utilized in sub-equation 1 in accordance with presentembodiments. It should be noted that Table II includes Fast ResponseMode constants and Table III includes Normal Response Mode constants.

TABLE II Constant Maximum Maximum Value (b) Maximum Intermediate SumVariable Variable Variable (Fast Term Value (sum of all Term Type Value(a) Preprocessing Mode) (a * b) previous rows) Overflow PeakDiffTdCf U8 100 None. This value may −29282 −2928200 −2928200 NO not exceed 100since the maximum SpO₂ value accepted is 100 SlopeRatio*SrCf U8  255None −1534 −391170 −3319370 NO FallSlope*FsCf S16 −32768 None −19 622592−2696778 NO PathRatio*PrCf U16 65535 None −7982 −523100370 −525797148 NOEq1Offset N/A N/A N/A 809250 809250 −524987898 NO

TABLE III Constant Maximum Maximum Value (b) Maximum Intermediate SumVariable Variable Variable (Normal Term Value (sum of all Term TypeValue (a) Preprocessing Mode) (a * b) previous rows) OverflowPeakDiffTdCf U8  100 None. This value may −33311 −3331100 −3331100 NOnot exceed 100 since the maximum SpO2 value accepted is 100SlopeRatio*SrCf U8  255 None −2151 −548505 −3879605 NO FallSlope*FsCfS16 −32768 None −706 23134208 19254603 NO PathRatio*PrCf U16 65535 None−6178 −404875230 −385620627 NO Eq1Offset N/A N/A N/A 576330 576330−385044297 NO

A second sub-equation, sub-equation D, may correspond to a differencebetween two consecutive reciprocations which have passed the hard limitqualifications checks, wherein consecutive reciprocations include tworeciprocations that are separated by less than a defined time span. Forexample, consecutive reciprocations may be defined as two reciprocationsthat are less than 120 seconds apart. The concept behind sub-equation Dmay be that ventilatory instability tends to be a relatively consistentevent, with little change from one reciprocation to the next. Artifactgenerally has a different signature and tends to be more random withgreater variation among reciprocations. For example, the followingequation may represent sub-equation D:

EqD=SlopeRatioDiff*SrDCf+DurationDiff*DDCf+NadirDiff*NdCf+PathLengthRatioDiff*PrDCf_(—) EqDOffset,

where, SrDCf, DDCf, NdCf, PrDCf, and EqDOffset may be selected usingleast squares analysis (e.g., using MATLAB®). With regard to othervariables in sub-equation D, SlopeRatioDiff may be defined as |CurrentRecip Slope Ratio−Slope Ratio of last qualified Recip|; DurationDiff maybe defined as |Current Recip Duration−Duration of last qualified Recip|;NadirDiff may be defined as |Current Recip Nadir−Nadir value of lastqualified Recip|; and PathLengthRatioDiff may be defined as |CurrentRecip Path Length Ratio−Path Length Ratio of last qualified Recip|.

With regard to sub-equation D, the tables (Tables IV and V) set forthbelow demonstrate that the inputs may be preprocessed to preventoverflow. Further, the tables set forth below include exemplary limitsthat may be utilized in sub-equation D in accordance with presentembodiments. It should be noted that Table IV includes Fast

Response Mode constants and Table V includes Normal Response Modeconstants.

TABLE IV Maximum Constant Intermediate Maximum Value (b) Maximum Sum(sum of Variable Variable Variable (Fast Term Value all previous TermType Value (a) Preprocessing Mode) (a * b) rows) Overflow EqDOffset N/AN/A N/A 885030 885030 885030 NO SlopeRatioDiff * SrDCf U8  255 None−2809 −716295 168735 NO DurationDiff * DDCf U16 240 The Recip −2960−710400 −541665 NO detection module may only detect recips less than orequal to 240 seconds long NadirDiff * NdCf U8  100 This value may −13237−1323700 −1865365 NO not exceed 100 since the maximum SpO2 valueaccepted is 100 PathLengthRatioDiff * PrDCf U16 65535 None −7809−511762815 −513628180 NO

TABLE V Maximum Constant Intermediate Maximum Value (b) Maximum Sum (sumof Variable Variable Variable (Normal Term Value all previous Term TypeValue (a) Preprocessing Mode) (a * b) rows) Overflow EqDOffset N/A N/AN/A 847650 847650 847650 NO SlopeRatioDiff * SrDCf U8  255 None −2629−670395 177255 NO DurationDiff * DDCf U16 240 The Recip −4282 −1027680−850425 NO detection module may only detect recips less than or equal to240 seconds long NadirDiff * NdCf U8  100 This value may −11705 −1170500−2020925 NO not exceed 100 since the maximum SpO2 value accepted is 100PathLengthRatioDiff * PrDCf U16 65535 None −7844 −514056540 −516077465NO

A third sub-equation, sub-equation 2, may combine the output ofsub-equation D with the output of sub-equation 1 for a reciprocation(e.g., a current reciprocation) and a previous reciprocation. Forexample, the following equation may represent sub-equation 2:

Eq2Score=EqDScore*DCf+Eq1ScoreCurrent*CurrEq1Cf+Eq1ScorePrev*PrevEq1Cf,

where DCf, N1Cf, PrevEq1Cf, and Eq2Offset may be selected using leastsquares analysis (e.g., using MATLAB®). With regard to other variablesin sub-equation 2, EqDScore may be described as the output ofsub-equation D; Eq1ScoreCurrent may be described as the output ofsub-equation 1 for a current reciprocation; and Eq1ScorePrev may bedescribed as the output of sub-equation 1 for the reciprocation previousto the current reciprocation.

With regard to sub-equation 2, the tables (Tables VI and VII) set forthbelow demonstrate that the inputs may be preprocessed to preventoverflow. Further, the tables set forth below include exemplary limitsthat may be utilized in sub-equation 2 in accordance with presentembodiments. It should be noted that Table VI includes Fast ResponseMode constants and Table VII includes Normal Response Mode constants.

TABLE VI Maximum Constant Intermediate Maximum Value (b) Maximum Sum(sum of Variable Variable Variable (Fast Term Value all previous TermType Value (a) Preprocessing Mode) (a * b) rows) Overflow Eq2Offset N/AN/A N/A −203800 −203800 −203800 NO EqDScore * DCf S32 −501590 Thelargest output 529 −265341110 −265544910 NO for sub-equation D may be−513628180 (see Table IV). The input value may be scaled by dividing thevalue by 1024. Therefore the largest input value may be −501590Eq1ScorePrev * PrevEq1cf S32 −512683 The largest output 333 −170723439−436268349 NO for sub-equation 1 may be −524987898 (see Table II). Theinput value may be scaled by dividing the value by 1024. Therefore thelargest input value may be −512683 Eq1ScoreCurrent * CurrEq1cf S32−512683 Same as previous 617 −316325411 −752593760 NO row

TABLE VII Maximum Constant Intermediate Maximum Value (b) Maximum Sum(sum of Variable Variable Variable (Normal Term Value all previous TermType Value (a) Preprocessing Mode) (a * b) rows) Overflow Eq2Offset N/AN/A N/A −194550 −194550 −194550 NO EqDScore * DCf S32 −503981 Thelargest output 532 −268117892 −268312442 NO for sub-equation D may be−516077465 (see Table V). The input value may be scaled by dividing thevalue by 1024. Therefore the largest input value may be −503981Eq1ScorePrev * PrevEq1Cf S32 −376000 The largest output 496 −186496000−454808442 NO for sub-equation 1 may be −385024297 (see Table III). Theinput value may be scaled by dividing the value by 1024. Therefore thelargest input value may be −376000 Eq1ScoreCurrent * CurrEq1cf S32−376000 Same as previous 406 −152656000 −607464442 NO row

A qualification function may utilize the output of each of the equationsdiscussed above (i.e., sub-equation 1, sub-equation D, and sub-equation2) to facilitate qualification and/or rejection of a potentialreciprocation. For example, the output of the qualification function maybe filtered with an IIR filter, and the filtered output of thequalification function may be used to qualify or reject a reciprocation.An equation for an unfiltered qualification function output inaccordance with present embodiments is set forth below:

QFUnfiltered=Eq1Score*SingleRecipWt*Eq2Cf+N2Score*MultipleRecipWt*Eq2Cf+NConsecRecip*ConsecCf+RecipMax*MaxCf+Artifact%*ArtCf+QFOffset,

where Eq2Cf, ConsecCf, MaxCf, ArtCf, and QFOffset may be selected usingleast squares analysis (e.g., using MATLAB®), and, as indicated above,Eq1Score may be defined as the output of sub-equation 1.

Other metrics in the unfiltered qualification function includeSingleRecipWt, MultipleRecipWt, NConsecRecip, RecipMax, and Artifact %.With regard to SingleRecipWt and MultipleRecipWt, when there are two ormore consecutive qualified reciprocations (e.g., qualifiedreciprocations that are less than 120 seconds apart) present,SingleRecipWt may equal 0 and MultipleRecipWt may equal 1. However, whenonly a single reciprocation is present, SingleRecipWt may equal 1 andMultipleRecipWt may equal 0.

NConseRecip, which may be defined as equal tomax(NConsecRecip′,QFConsecMax), may include a count of the number ofconsecutive reciprocations (e.g., reciprocations that are less than orequal to 120 seconds apart) that have passed the hard limit checks. Thevalue for NConsecRecip may be reset to 0 whenever a gap between any twopartially qualified reciprocations exceeds 120 seconds. This may bebased on the fact that ventilatory instability is a relatively longlasting event as compared to artifact. Therefore, as more reciprocationspass the hard limit checks, the qualification function may beginqualifying reciprocations that were previously considered marginal.However, to guard against a situation where something is causing alonger term artifact event (e.g., interference from nearby equipment),the value may be clipped to a maximum value to limit the metricsinfluence on the qualification function output.

RecipMax, which may be defined as equal to max(Fall Peak, Rise Peak),may facilitate making decisions about marginal reciprocations. Indeed,marginal reciprocations with higher maximum SpO₂ values may be morelikely to get qualified than marginal reciprocations with lower SpO₂values. It should be noted that this metric works in tandem with theNConsecRecip metric, and multiple marginal reciprocations with lowermaximum SpO₂ values may eventually, over a long period of time, getqualified due to the NConsecRecip metric.

The metric Artifact % may be defined as an artifact percentage that isequal to 100*Total Artifact Count/Recip Duration, where Total ArtifactCount is the number of times and artifact flag was set during thereciprocation. Present embodiments may include many metrics andequations that are used to set the artifact flag. Because of this it isa generally reliable indication of the amount of artifact present in theoximetry system as a whole. Marginal reciprocations with a high Artifact% are less likely to be qualified than marginal reciprocations with alow (or 0) artifact percentage.

A last component of the qualification function may include an infiniteimpulse response (IIR) filter that includes coefficients that may betuned manually using a tool (e.g., a spreadsheet) that models algorithmperformance. The filtered qualification function may be represented bythe following equation, which includes different constants for differentmodes (e.g., Fast Response Mode and Normal Response Mode):

QFFiltered=SingleRecipWt*QFUnfiltered+((1−a)*QFUnfiltered+a*PrevQFFiltered)*MultipleRecipWt,

where QFUnfiltered may be defined as the current unfilteredqualification function output; PrevQFFiltered may be defined as theprevious filtered qualification function output; and where the constat“a” may be set to 0.34 for Fast Response Mode and 0.5 for NormalResponse Mode.

The filtered output of the qualification function may be compared to athreshold to determine if the current reciprocation is the result of RAFor artifact. The optimum threshold may theoretically be 0.5. However, animplemented threshold may be set slightly lower to bias the output ofthe qualification function towards qualifying more reciprocations, whichmay result in additional qualification of false positives. The thresholdmay be lowered because, in accordance with present embodiments, acluster determination portion of the algorithm, such as may be performedby the CD feature 206, may require a certain number (e.g., 5) of fullyqualified reciprocations before an index may be calculated, and acertain number (e.g., at least 2) of consecutive qualifiedreciprocations (with no intervening disqualified reciprocations) withinthe set of fully qualified reciprocations. Since multiple reciprocationsmay be required, the clustering detection method may be biased towardfiltering out false positives. Accordingly, the reciprocationqualification function threshold may be lowered to balance the twoprocesses.

The CD feature 206 may be capable of performing an algorithm thatmaintains an internal reciprocation counter that keeps track of a numberof qualified reciprocations that are currently present. When thereciprocation counter is greater than or equal to a certain value, suchas 5, the clustering state may be set to “active” and the algorithm maybegin calculating and reporting the SPDi. When clustering is not active(e.g., reciprocation count<5) the algorithm may not calculate the SPDi.The SPDi may be defined as a scoring metric associated with theidentification of a saturation trend pattern generated in accordancewith present embodiment and may correlate to ventilatory instability ina population of sleep lab patients.

The CD feature 206 may utilize various rules to determine thereciprocation count. For example, when the clustering state is inactive,the following rules may be observed:

-   -   1.) If the distance between qualified reciprocation exceeds 120        seconds, then the reciprocation count=0;    -   2.) If the current reciprocation is qualified, and the time from        the start of the current reciprocation to the end of the last        qualified reciprocation is <=120 seconds, then the reciprocation        count=reciprocation count+1;    -   3.) If the current reciprocation is not qualified, then the        reciprocation count=max(reciprocation count−2, 0).        Once clustering is active, it may remain active until the time        between two qualified reciprocations exceeds 120 seconds. The        following table (Table II) illustrates an example of how the        reciprocation count rules may be applied to determine a        clustering state.

TABLE VIII Current Time Since Last Reciprocation Qualified ReciprocationReciprocation Clustering Qualified (seconds) Count State TRUE N/A 1INACTIVE FALSE 60 0 INACTIVE TRUE N/A 1 INACTIVE FALSE 60 0 INACTIVETRUE N/A 1 INACTIVE TRUE 30 2 INACTIVE TRUE 120  3 INACTIVE FALSE 60 1INACTIVE TRUE 10 2 INACTIVE TRUE 20 3 INACTIVE TRUE 40 4 INACTIVE FALSE30 2 INACTIVE FALSE 60 0 INACTIVE TRUE N/A 1 INACTIVE TRUE 20 2 INACTIVETRUE 120  3 INACTIVE TRUE 10 4 INACTIVE FALSE 90 2 INACTIVE TRUE 120  3INACTIVE TRUE 60 4 INACTIVE TRUE 20 5 ACTIVE TRUE 30 6 ACTIVE FALSE 50 6ACTIVE FALSE 100  6 ACTIVE TRUE 121  1 INACTIVE FALSE 50 0 INACTIVE TRUEN/A 1 INACTIVE TRUE 30 2 INACTIVE TRUE 121  1 INACTIVE TRUE 10 2INACTIVE TRUE 20 3 INACTIVE TRUE 40 4 INACTIVE TRUE 40 5 ACTIVE

When the clustering state is active, the SPDi calculation feature 208may calculate an unfiltered SPDi for each new qualified reciprocation.The following formula may be used by the SPDi calculation feature 208:

Unfiltered SPDi=a*Magnitude+b*PeakDelta+c*NadirDelta;

-   -   wherein a=1.4, b=2.0, c=0.2;    -   wherein Magnitude=average magnitude of all reciprocations in the        last 6 minutes;    -   wherein PeakDelta=average of the three highest qualified        reciprocation rise peaks in the last 6 minutes minus the average        of the three lowest qualified reciprocation rise peaks in the        last 6 minutes; and    -   wherein NadirDelta=average of the three highest qualified        reciprocation nadirs in the last 6 minutes minus the average of        the three lowest qualified reciprocation nadirs in the last 6        minutes.

Wherein SPDi<=31

The above formula may be utilized to quantify the severity of aventilatory instability pattern. The constants and metrics used may bebased on input from clinical team members. It should be noted that thePeakDelta parameter may be assigned the largest weighting constant sincethe most severe patterns generally have peak reciprocation values thatdo not recover to the same baseline.

The unfiltered SPDi may be updated whenever clustering is active and anew qualified reciprocation is detected. Non-zero SPDi values may belatched for a period of time (e.g., 6 minutes). The unfiltered SPDi maythen be low pass filtered to produce the final output SPDi value. Thefollowing IIR filter with a response time of approximately 40 secondsmay be used:

SPDi=Unfiltered SPDi/a+Previous Filtered SPDi*(a−1)/a;

wherein a=40.

FIG. 6 is an exemplary graph 260 including an SpO₂ trend 262 thatcontains a ventilatory instability SpO₂ pattern and a trend of theresulting SPDi 264. In the illustrated example, it should be noted thatthe SPDi is sensitive to the decreasing peaks (incomplete recoveries)starting at approximately t=6000.

The UN feature 210 may be capable of determining if a user notificationfunction should be employed to notify a user (e.g., via a graphical oraudible indicator) of the presence of a detected patterns such asventilatory instability. The determination of the UN feature 210 may bebased on a user configurable tolerance setting and the current value ofthe SPDi. For example, the user may have four choices for thesensitivity or tolerance setting: Off, Low, Medium, and High. When thesensitivity or tolerance setting is set to Off, an alarm based ondetection of a saturation pattern may never be reported to the user. Theother three tolerance settings (i.e., Low, Medium, and High) may eachmap to an SPDi threshold value. For example, Low may map to an SPDithreshold of 6, Medium may map to an SPDi threshold of 15, and High maymap to an SPDi threshold of 24. The thresholds may be based on inputfrom users. When the SPDi is at or above the threshold for a giventolerance setting, the user may be notified that ventilatory instabilityis present. As discussed below, the indication to the user may include agraphical designation of the trend data corresponding to the detectedpattern. For example, the trend data utilized to identify a ventilatoryinstability pattern may be highlighted, flashing, or otherwise indicatedon a user interface of a monitor in accordance with present embodiments.Similarly, parameters such as the SPDi value and the tolerance settingsmay be graphically presented on a display.

In embodiments, the display may include a graphical indicator that mayprovide information to a user related to the occurrence, frequency,and/or magnitude of the patterns detected. The information may be basedon the SPDi index, which is proportional to the magnitude andvariability of qualified reciprocations. The SPD calculation feature maybe capable of notifying a user of ventilatory instability thatcorresponds to a certain SPDi index value. In embodiments, when the SPDiis at or above a threshold setting, the user may be notified via agraphical indicator 600.

As illustrated in FIG. 7, the graphical indicator 600 may be representedon display 598 as a dashed triangle that may graphically fill from topto bottom as a monitored and/or calculated value increases. For example,in one embodiment, the graphical indicator 600 may gradually fill as theSPDi index calculated by the SPDi calculation feature 208 increases.Further, the graphical indicator 600 may include a tolerance levelindicator 602 that displays an index, for example 1, 2, or 3, fortolerance or sensitivity settings of High, Medium, and Low,respectively, for the SPDi calculation feature 208. The tolerancesettings may set the threshold for triggering a change in the graphicalindicator 600 and/or for triggering SPD-associated alarms. As shown inFIG. 9, the graphical indicator 600 may be empty, indicating that anSPDi index is below a certain threshold.

In addition, the display 598 may also include additional indicators,such as a Sat Seconds indicator 604 that relates to oxygen saturationinformation. Sat Seconds indicators may assist clinicians in focusing ondesaturations related to a patient condition rather than shortdesaturations that may be the result of measurement anomalies. As shown,the Sat Seconds indicator 604 may be partially full while the graphicalindicator 600 is empty. The Sat Seconds indicator 604 may displayresults determined by a Sat Second analyzing function, which in anembodiment analyzes desaturation events by multiplying their duration(seconds) by the number of percentage points the patient exceeds thealarm limit. In an embodiment, the Sat Seconds analyzer may determine ifan oxygen desaturation event has occurred by analyzing a plot of oxygensaturation versus time. The Sat Seconds analyzer may integrate the areaunder the curve of time spent below a certain oxygen saturationthreshold. Accordingly, sudden, short desaturation readings that may bemeasurement noise (e.g., that otherwise may trigger nuisance alarms) maybe eliminated from a Sat Seconds counter clock while more prolongeddesaturations may be counted. Clinicians can set the SatSeconds limit,or clock, to 10, 25, 50 or 100 SatSeconds. In an embodiment, the clockmay be set to 100, and therefore only events that equal or surpass the100 SatSeconds limit may trigger an alarm. In addition, the Sat Secondsindicator 604 may fill up in relation to the Sat Seconds count. Forexample, the indicator 604 may be full when the count reaches 100.

While the Sat Seconds indicator 604 may manage nuisance alarms relatedto desaturation events, the graphical indicator 600 may displayinformation determined by not only the duration and magnitude of theoxygen desaturation, but also to the patterns of the desaturationevents, as provided herein. Such analysis may provide information to thehealthcare provider about ventilatory instability that may, for example,be related to sleep apnea. Turning to the graphical indicator 600, whichprovides information to a clinician related to ventilatory instability,FIG. 8 shows a display screen 620 in which the graphical indicator 600has started to fill up from the bottom. The “filling up” may representthe addition of a fill (e.g., any color pixels) to the area of thetriangle. In one embodiment, the graphical indicator 600 may fill upwhen the calculated SPDi index is higher than a tolerance setting. Asnoted, the High Tolerance, Medium Tolerance, and Low Tolerance alarmlimits may refer to certain default values of the SPDi index, such as24, 15, and 6, respectively. When the SPDi index is higher than, forexample, 24 (High Tolerance setting), the graphical indicator 600 maybegin to fill. In an embodiment, the graphical indicator 600 may beginto fill up when the SPDi index is lower than but near 24, whereby anSPDi index of 24 represents a “full” state. In such an embodiment, theapproximately 25% full graphical indicator as shown may represent anSPDi index of, for example, 18.

FIG. 9 is a display 640 including an indicator 600 that is approximately50% full. As noted, the graphical indicator 600 may continue to fill asthe SPDi index rises over time. The SPDi index may be calculated over arolling period of time. In embodiments, the SPDi index may be calculatedover a 240 second window. If, during this window of time, the SPDi indexincreases as a result an increase in measured recip frequency ormagnitude parameters used to determine the index, the graphicalindicator 600 may continue to fill up.

FIG. 10 is an exemplary display 660 showing a graphical indicator 600that is approximately 75% full, and FIG. 11 is an exemplary display 680showing a graphical indicator 600 that is approximately 100% full. Asshown in FIGS. 7-11, the indicator 600 may fill up as a percentage orfraction of the total indicator space as the SPDi index increases. Forexample, the indicator 600 may have five possible display states: empty,25% full, 50% full, 75% full, or 100% full. In embodiments, theindicator 600 may fill in any suitable manner. For example, a graphicalindicator may have any number of fill states, e.g., filling up in 10%,20%, 25%, or 50% increments. In other embodiments, the indicator 600 mayalso change in intensity to indicate increasing ventilatory instability.For example, an indicator may fill in uniformly, but with increasingintensity, as the SPDi index increases. In an embodiment, the indicator600 may have states that resemble different values on a grayscale, withthe percentage grayscale increasing at the SPDi index increases.

A filled state of the graphical indicator 600 may trigger a primary orsecondary alarm. In an embodiment, a primary alarm, such as a textalert, may be triggered when the graphical indicator 600 begins to fill.When the indicator 600 has reached a full state, a secondary alarm, suchas an audio alarm, may then be triggered.

The indicator 600 may be displayed on any number of monitor views toprovide information to a healthcare provider during various monitoringactivities. FIG. 12 shows an exemplary general pleth display 700 with aplethysmographic waveform 702. The display 700 may include a graphicalindicator 600 for saturation pattern detection with a toleranceindicator 602. The display may also include softkeys 704 for navigatingbetween other display views.

FIG. 13 shows an exemplary blip display 720. As shown, the location ofthe graphical indicator 600 on the screen may change according to theparticular display view chosen. However, the general shape of theindicator 600 may remain substantially the same so that the user mayeasily identify the indicator 600. FIG. 14 shows an exemplary generalcare format view 760. As shown, the graphical indicator 600 and the SatSeconds indicator 604 may be relatively larger in certain views. FIG. 15shows a real-time trend display 780 with a trend xy plot 782. FIG. 16shows a display 786 in which an SPD event788 is highlighted on the xyplot 782. In FIG. 15 and FIG. 16, the graphical indicator 600 may bedisplayed along with other indicators and patient data.

In embodiments, a user may have the ability to change certain settingson the monitor 10 related to the graphical indicator 600. In oneembodiment, a user may be able to change settings related to SPD alarmlimits. An alarm setup display related to the SPD alarm settings may beaccessed via softkey from other display screens. FIG. 17 is an exemplaryalarm setup display 800. As shown, a user may be able to select anoption in which the monitor 10 activates SPD calculation features andassociated indicators and alarms. In addition, a user may activate a SatSeconds calculation and/or display feature. In an embodiment, a user maybe able to select between audio and/or visual alarms in response tosaturation pattern detection by the monitor 10, as shown in FIG. 18,which depicts a display 820 in which a user may select to turn off audioalerts related to saturation pattern detection.

In another embodiment, a user may be able to change the default valueson the limits to user-selected values. FIG. 19 is an exemplary display840 showing an SPD Tolerance menu. A user may select between multipleSPD tolerance settings for High, Medium, or Low Tolerance of theSPD-associated alarms. In an embodiment, a monitor 10 may store certaindefault values associated with SPDi index values. These default valuesmay be determined based on clinical observations of a test patientpopulation or other input from healthcare providers. For example, thedefault High Tolerance value may be associated with an SPDi index valueof 24. Accordingly, any SPD-associated alarms may not trigger until theSPDi index for a calculated window of time is at or near 24.

In another embodiment, a user may input specific values for High,Medium, and Low Tolerance limits. A user may select any value, so longas the High Tolerance limit is higher than the Medium Tolerance limit,and the Medium Tolerance limit is higher than the Low Tolerance limit. Amonitor 10 may be able trigger an error message if a user attempts toset a limit of less than zero or if a user attempts to set a HighTolerance limit that is lower than a Medium Tolerance limit, and so on.

FIG. 20 is a flow chart 900 indicating how a monitor 10 may triggeralarms based on the SPDi tolerance settings. At start 902, if atolerance setting is set to “OFF” at 904, the process sets the alarmstatus to “NO SPD ALARM” at 905. If the tolerance is set to Low (906),Medium (908), or High (910), the SPDi index is compared to theappropriate threshold, depending on the setting. For example, if thetolerance is set to Low at 906, the SPDi index is compared to the LowIndex Limit at 912. If the SPDi index is lower that the Low Index Limit,the process may set the alarm status to “NO SPD ALARM” at 905. If theSPDi index is higher than the Low Index Limit, the process may thendetermine if audio alerts have been enabled at 914. If such alerts havenot been enabled, the process set the alarm status to “VISUAL ONLY” totrigger visual alarms at 916. If audible alerts have been enabled, thealarm status may be set to “AUDIBLE VISUAL” at 918 for triggeringaudible and visual alarms before the process ending at 920. Similarly, aMedium Tolerance setting may be compared to a Medium Index Limit at 922and a High Tolerance setting may be compared to a High Index Limit at924.

While the embodiments of the present disclosure may be susceptible tovarious modifications and alternative forms, specific embodiments havebeen shown by way of example in the drawings and will be described indetail herein. However, it should be understood that the presentembodiments are not intended to be limited to the particular formsdisclosed. Rather, present embodiments are to cover all modifications,equivalents and alternatives falling within the spirit and scope ofpresent embodiments as defined by the following appended claims.

1.-19. (canceled)
 20. A pulse oximeter, comprising: an input forreceiving a photoplethysmograph (PPG) signal from a pulse oximetrysensor, wherein the pulse oximetry sensor detects light attenuated by apatient; non-transitory computer-readable medium comprising: computerprogram instructions recorded thereon for causing the pulse oximeter to:process the PPG signal to generate oxygen saturation data, analyze theoxygen saturation data to detect reciprocations in the oxygen saturationdata, each reciprocation defined by a fall peak, a nadir, and a risepeak, qualify each of the detected reciprocations based on qualificationcriteria, maintain a count of qualified reciprocations, and determine anoccurrence of a clustering state indicative of a presence of ventilatoryinstability based on the count; and a display for displaying aventilatory instability notification while the clustering state isdetermined to be occurring.
 21. The pulse oximeter of claim 20, whereinthe non-transitory computer-readable medium further comprises computerprogram instructions recorded thereon for causing the pulse oximeter todetermine a scoring metric associated with consecutive qualifiedreciprocations.
 22. The pulse oximeter of claim 21, wherein thenon-transitory computer-readable medium further comprises computerprogram instructions recorded thereon for causing the pulse oximeter todetermine the scoring metric while the clustering state is determined tobe occurring.
 23. The pulse oximeter of claim 21, wherein thenon-transitory computer-readable medium further comprises computerprogram instructions recorded thereon for causing the pulse oximeter totrigger an alarm when the scoring metric reaches a threshold.
 24. Thepulse oximeter of claim 20, wherein the count of qualifiedreciprocations is maintained over a time period.
 25. The pulse oximeterof claim 20, wherein the count of qualified reciprocations is maintainedover a time period determined based on a length of a qualifiedreciprocation.
 26. The pulse oximeter of claim 20, wherein thequalification criteria comprise a fall magnitude of the detectedreciprocations.
 27. The pulse oximeter of claim 20, wherein thequalification criteria comprise a slope ratio of the detectedreciprocations.
 28. The pulse oximeter of claim 20, wherein thequalification criteria comprise a path length ratio of the detectedreciprocations.
 29. The pulse oximeter of claim 20, wherein thequalification criteria comprise: fall magnitude of the detectedreciprocations, slope ratio of the detected reciprocations, and pathlength ratio of the detected reciprocations.
 30. The pulse oximeter ofclaim 20, wherein the qualification criteria comprise a linearqualification function.
 31. The pulse oximeter of claim 20, whereindetecting reciprocations in the oxygen saturation data comprises:calculating an upper band and a lower band based on a rolling mean ofthe oxygen saturation data and a standard deviation of the oxygensaturation data; and identifying peaks in the oxygen saturation databased on the upper band and the lower band.
 32. A pulse oximetry system,comprising: an input for receiving a photoplethysmograph (PPG) signalfrom a pulse oximetry sensor, wherein the pulse oximetry sensor detectslight attenuated by a patient; circuitry configured to: determine oxygensaturation of the patient based on the PPG signal; detect reciprocationsbased on the oxygen saturation of the patient, each reciprocationdefined by a fall peak, a nadir, and a rise peak; apply qualificationcriteria to each of the detected reciprocations; determine an occurrenceof a clustering state when at least two consecutive reciprocations arequalified; and a display for displaying a ventilatory instabilitynotification while the clustering state is determined to be occurring.33. The pulse oximetry system of claim 32, wherein the circuitry isfurther configured to determine a scoring metric associated withconsecutive qualified reciprocations.
 34. The pulse oximetry system ofclaim 33, wherein the circuitry is further configured to determine thescoring metric while the clustering state is determined to be occurring.35. The pulse oximetry system of claim 33, wherein the circuitry isfurther configured to trigger an alarm when the scoring metric reaches athreshold.
 36. The pulse oximetry system of claim 32, wherein thecircuitry is further configured to maintain the count of qualifiedreciprocations over a time period.
 37. The pulse oximetry system ofclaim 32, wherein the circuitry is further configured to maintain thecount of qualified reciprocations over a time period determined based ona length of a qualified reciprocation.
 38. The pulse oximetry system ofclaim 32, wherein the qualification criteria comprise a fall magnitudeof the detected reciprocations.
 39. The pulse oximetry system of claim32, wherein the qualification criteria comprise a slope ratio of thedetected reciprocations.
 40. The pulse oximetry system of claim 32,wherein the qualification criteria comprise a path length ratio of thedetected reciprocations.
 41. The pulse oximetry system of claim 32,wherein the qualification criteria comprise: fall magnitude of thedetected reciprocations, slope ratio of the detected reciprocations, andpath length ratio of the detected reciprocations.
 42. The pulse oximetrysystem of claim 32, wherein the qualification criteria comprise a linearqualification function.
 43. The pulse oximetry system of claim 32,wherein detecting reciprocations comprises: calculating an upper bandand a lower band based on a rolling mean of the oxygen saturation of thepatient and a standard deviation of the oxygen saturation of thepatient; and identifying peaks in the oxygen saturation of the patientbased on the upper band and the lower band.
 44. A pulse oximeter,comprising: an input for receiving a photoplethysmograph (PPG) signalfrom a pulse oximetry sensor, wherein the pulse oximetry sensor detectslight attenuated by a patient; means for detecting a presence ofventilatory instability; and a display for displaying a ventilatoryinstability notification when the presence of ventilatory instability isdetected.
 45. The pulse oximeter of claim 44, wherein the means fordetecting the presence of ventilatory instability comprisenon-transitory computer-readable medium comprising: computer programinstructions recorded thereon for causing the pulse oximeter to: processthe PPG signal to generate oxygen saturation data, analyze the oxygensaturation data to detect reciprocations in the oxygen saturation data,each reciprocation defined by a fall peak, a nadir, and a rise peak,qualify each of the detected reciprocations based on qualificationcriteria, maintain a count of qualified reciprocations, and determine anoccurrence of a clustering state indicative of the presence ofventilatory instability based on the count.
 46. A method for determiningventilatory instability by a pulse oximeter, comprising: receiving,using an input of the pulse oximeter, a photoplethysmograph (PPG) signalfrom a pulse oximetry sensor, wherein the pulse oximetry sensor detectslight attenuated by a patient; determining, using the pulse oximeter,oxygen saturation of the patient based on the PPG signal; detecting,using the pulse oximeter, reciprocations based on the oxygen saturationof the patient, each reciprocation defined by a fall peak, a nadir, anda rise peak; applying, using the pulse oximeter, qualification criteriato each of the detected reciprocations; determining, using the pulseoximeter, an occurrence of a clustering state when at least twoconsecutive reciprocations are qualified; and displaying, using adisplay of the pulse oximeter, a ventilatory instability notificationwhen the clustering state is determined to be occurring.